1. Field of the Invention
The present invention relates to a mobile station such as a mobile telecommunication station, a personal digital assistant (PDA), etc., provided with a liquid crystal display (LCD) as a display device, and more particularly, to an apparatus for controlling the backlight in a mobile station provided with a color LCD.
2. Discussion of the Related Art
A mobile station, which is in wide use these days, generally includes a plurality of keys for various functions, an LCD, and an LCD backlight for lightening the display of the LCD. While the mobile station is operated and/or the keys are manipulated, the operation according to such manipulation and the data such as input letters, etc., are displayed on the LCD, and further, the information such as date or time, etc., may be also displayed. The battery power provided for the mobile station is supplied to the LCD and the LCD backlight.
In the meantime, in view of the fact that the mobile station uses a chargeable battery as its primary operation power source, efforts have been made to extend the maximum allowable operation time of its battery once the battery is charged. The efforts may be classified into two general categories. First, methods of increasing the charge capacity of the battery, and second methods of reducing the power consumed during the operation of the mobile station. In particular, since a large amount of power is consumed for operating the LCD backlight, a method for reducing the consumed power by properly controlling the backlight of the LCD is being developed.
There are two types of methods typically used as a technology to reduce the electric current for driving the backlight in the conventional mobile station (so called “dimming technology”), which are as follows. One is to forcibly turn off the LCD backlight if there is no input during the operation of the mobile station for a predetermined time, and the other is to turn on/off the output of a backlight drive for driving the backlight by means of an appropriate frequency by using a pulse width modulation (PWM) signal in a control unit of the mobile station.
However, in case of a color LCD, unlike a normal black and white LCD and a gray LCD, a displayed image can be recognized only when light is transmitted through the backlight, and therefore, in the case of using the method of forcibly turning off the backlight in the dimming technology, it has disadvantages that a user cannot see the display, and the user may mistake the absence of the display the mobile station being turned off.
In addition, the method of using the PWM signal requires the generation of the PWM signal in the control unit of the mobile station in the dimming mode, but sometimes the control unit fails to generate the PWM signal, such as during the operation in a sleep mode of the mobile station and therefore, the dimming mode cannot be effectively operated.